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[195.135.220.15]) by mx.google.com with ESMTPS id n46si6052445edd.310.2019.04.24.00.58.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Apr 2019 00:58:37 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 25D96AE2B; Wed, 24 Apr 2019 07:58:36 +0000 (UTC) Date: Wed, 24 Apr 2019 09:58:34 +0200 From: Michal Hocko To: Yang Shi Cc: vbabka@suse.cz, rientjes@google.com, kirill@shutemov.name, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [v2 PATCH] mm: thp: fix false negative of shmem vma's THP eligibility Message-ID: <20190424075834.GB12751@dhcp22.suse.cz> References: <1556037781-57869-1-git-send-email-yang.shi@linux.alibaba.com> <20190423175252.GP25106@dhcp22.suse.cz> <6004f688-99d8-3f8c-a106-66ee52c1f0ee@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 23-04-19 17:22:36, Yang Shi wrote: > > > On 4/23/19 11:34 AM, Yang Shi wrote: > > > > > > On 4/23/19 10:52 AM, Michal Hocko wrote: > > > On Wed 24-04-19 00:43:01, Yang Shi wrote: > > > > The commit 7635d9cbe832 ("mm, thp, proc: report THP eligibility > > > > for each > > > > vma") introduced THPeligible bit for processes' smaps. But, when > > > > checking > > > > the eligibility for shmem vma, __transparent_hugepage_enabled() is > > > > called to override the result from shmem_huge_enabled().  It may result > > > > in the anonymous vma's THP flag override shmem's.  For example, > > > > running a > > > > simple test which create THP for shmem, but with anonymous THP > > > > disabled, > > > > when reading the process's smaps, it may show: > > > > > > > > 7fc92ec00000-7fc92f000000 rw-s 00000000 00:14 27764 /dev/shm/test > > > > Size:               4096 kB > > > > ... > > > > [snip] > > > > ... > > > > ShmemPmdMapped:     4096 kB > > > > ... > > > > [snip] > > > > ... > > > > THPeligible:    0 > > > > > > > > And, /proc/meminfo does show THP allocated and PMD mapped too: > > > > > > > > ShmemHugePages:     4096 kB > > > > ShmemPmdMapped:     4096 kB > > > > > > > > This doesn't make too much sense.  The anonymous THP flag should not > > > > intervene shmem THP.  Calling shmem_huge_enabled() with checking > > > > MMF_DISABLE_THP sounds good enough.  And, we could skip stack and > > > > dax vma check since we already checked if the vma is shmem already. > > > Kirill, can we get a confirmation that this is really intended behavior > > > rather than an omission please? Is this documented? What is a global > > > knob to simply disable THP system wise? > > > > > > I have to say that the THP tuning API is one giant mess :/ > > > > > > Btw. this patch also seem to fix khugepaged behavior because it > > > previously > > > ignored both VM_NOHUGEPAGE and MMF_DISABLE_THP. > > Second look shows this is not ignored. hugepage_vma_check() would check this > for both anonymous vma and shmem vma before scanning. It is called before > shmem_huge_enabled(). Right. I have missed the earlier check. The main question remains though. -- Michal Hocko SUSE Labs